Media capable of patterning by light exposure are a common manifestation of information storage. In one of the oldest techniques, photographic emulsions are used to record the image of the light incident upon it. There is recently an increased demand for storage of information by optical means, for use in archiving, security tags, 3D representation of images, aberration correction, and storage of digital data. In order to achieve the desired optical response or a larger optical response, 3D media are used. Furthermore, the areal information capacity is limited by the optics of the read/write system. For example, holographic stereograms require small lateral features to achieve high image resolution, as well as thick media to achieve large image contrast. Additional increases in capacity require additional dimensions, which might include the spatial thickness dimension, but also could include color, polarization, or phase multiplexing.
The main approaches to entry into the third spatial dimension involve either multilayer information storage or holographic information storage. Multilayer storage can be affected either by physical layers, or optical layering provided by localization near the focus of the lasers using multiphoton absorption. These approaches, however, have significant limitations. Holographic storage requires complicated and potentially costly optical read/write hardware. Similarly, the lasers needed for multiphoton absorption are more complicated, costly, and introduce additional sources of noise. Physical multilayering employs simpler hardware, but the manufacturing of multiple layers in the storage medium has proven to be difficult to scale up economically.